This study documents the differences in kinetics of 2 h (n = 7) and 4 h (n = 9) of 1.25 minimum alveolar anesthetic concentration (MAC) of desflurane (9.0%) versus (on a separate occasion) sevoflurane (3.0%), both administered in a fresh gas inflow of 2 L/min, These data are extensions of our previous g-h (n = 7) studies of these anesthetics. By 10 min of anesthetic administration, average inspired (F-1 and end-tidal concentration (F-A) (F-I/F-A; the inverse of the more commonly used F-A/F-I) decreased to less than 1.15 for both anesthetics, with the difference from 1.0 nearly twice as great for sevoflurane as for desflurane. During all sevoflurane administrations, F-A/F-I for Compound A [CH2F-O-(=CF2) CF3); a vinyl ether resulting from the degradation of sevoflurane by Baralyme(R)] equaled approximately 0.8, and the average inspired concentration equaled approximately 40 ppm. Compound A is of interest because at approximately 150 ppm-h, it san Induce biochemical and histological evidence of glomerular and tubular injury in rats and humans. During elimination, F-A/F-A0 F-A0 for Compound A (F-A0 is the last end-tidal concentration during anesthetic administration) decreased abruptly to 0 after 2 h and),h of anesthesia and to approximately 0.1 (F-A approximately 3 ppm) after 8 h of anesthesia. In contrast, F-A/F-A0 for desflurane and sevoflurane decreased in a conventional, multiexponential manner, the decrease being increasingly delayed with increasing duration of anesthetic administration. F-A/F-A0 for sevoflurane exceeded that for desflurane for any given duration of anesthesia, and objective and subjective measures indicated a faster recovery with desflurane. Times (mean +/- SD) to initial response to command (2 h 10.9 +/- 1.2 vs 17.8 +/- 5.1 min, 4 h 11.3 +/- 2.1 vs 20.8 +/- 4.8 min, 8 h 14 +/- 4 vs 28 +/- 8 min) and orientation (2 h 12.7 +/- 1.6 vs 21.2 +/- 4.6 min, 4h 14.8 +/- 3.1 vs 25.3 +/- 6.5 min, 8 h 19 +/- 4 vs 33 +/- 9 min) were shorter with desflurane. Recovery as defined by the digit symbol substitution test, P-deletion test, and Trieger test results was more rapid with desflurane. The incidence of vomiting tvas greater with sevoflurane after 8 h of anesthesia but not after shorter durations. We conclude that for each anesthetic duration, F-1 more closely approximates F-A with desflurane during anesthetic administration, F-A/F-A0 decreases more rapidly after anesthesia with desflurane, and objective measures indicate more rapid recovery with desflurane. Finally, it seems that after 2-h and 4-h administrations, all Compound A taken up is bound within the body. Implications: Regardless of the duration of anesthesia, elimination is faster and recovery is quicker for the inhaled anesthetic desflurane than far the inhaled anesthetic sevoflurane. The toxic degradation product of sevoflurane, Compound A, seems to bind irreversibly to proteins in the body.
